Valve, and the use thereof for a clutch

ABSTRACT

A valve, in particular proportional pressure regulating valve, having a valve piston ( 12 ) which is guided in longitudinally movable fashion in a valve housing ( 10 ) and which can be actuated by means of an operation device ( 14 ), wherein the valve housing ( 10 ) has multiple fluid ports (P, A, T) and wherein, in one movement position of the valve piston ( 12 ), a fluid-conducting connection is produced between a pressure supply port (P) and a working port (A), and in another movement position, a further fluid-conducting connection is produced between the working port (A) and a tank port (T), is distinguished by the fact that the respective pressure difference that arises between the working port (A) and the tank port (T) as flow passes through the further fluid-conducting connection acts, by way of an actuation device ( 30 ), on the valve piston ( 12 ) such that the latter passes from a stop position ( 32 ), proceeding from which the further fluid-conducting connection is substantially shut off, into a fully open opening position, in which, in relation to the stop position ( 32 ), an enlarged opening cross section from working port (A) to tank port (T) is realized.

The invention relates to a valve, in particular to a proportionalpressure regulating valve, having a valve piston guided longitudinallydisplaceably in a valve housing and controllable by means of an actuatordevice, wherein the valve housing has several fluid ports and wherein,in a movement position of the valve piston, a fluid-carrying connectionis establishable between a pressure supply port and a utility port and,in another driving position, another fluid-carrying connection betweenthe utility port and a tank port is establishable. The invention furtherrelates to the use of such a valve in clutches.

Such valves in the form of so-called proportional pressure regulatingvalves are widely used for mobile working devices for theelectro-hydraulic control of clutches.

These clutches must be filled regularly with an operating fluid in theform of oil when activated initially until their friction surfaces reachthe point of contact in order to be able to act as a clutch. To thisend, spring forces must be overcome in the clutch. The pressures createdby spring forces are often very low (less than 2 bar), and a furtherincrease in the clutch pressure then results in normal forces on theclutch linings, which can ultimately transmit the torque throughfrictional forces.

These low spring forces result in problems when switching off theclutches because, in order to move the respective clutch disc away fromthe assignable contact surface, only the pressure caused by these springforces is available to produce the oil flow through the proportionalpressure regulating valves.

There is therefore a requirement for these valves that the pressure lossin the flow from the working port to the tank port should be extremelysmall because that is the only way to ensure fast and safe switching offof the clutch.

In the current prior art, the largest possible flow cross-section isopened in directly controlled proportional pressure regulating valvesthrough the use of magnets with large working strokes. At the same time,this requires as much magnetic force as possible in order not to let theratio between magnetic force and flow force become too unfavorable.Large and expensive actuator devices in the form of actuating magnetsare therefore required.

If one were now to overcome these disadvantages by using smaller, andthus more economical actuating magnets with the same force, which iswithin the average skill of a person skilled in the art in the field ofvalve and clutch technology, it would necessarily decrease the length ofthe linear force-stroke range. If one does not intend to reduce the fullopening cross-section for the fast emptying of the fluid medium from theclutch, one must not shorten the actual valve stroke of the valvepiston, but this in turn inevitably results in the spring forces holdingthe actuating magnet in its non-linear force range when the valve isswitched on, requiring a large magnet current for “breaking away themagnet” from the end position.

At the moment, however, where the magnetic force becomes greater thanthe spring force, one moves on the strongly ascending branch of thecharacteristic force-stroke line and the balance between magnetic forceand spring force would be lost in favor of the magnetic force. On the PIcharacteristic line of the valve this would be noticeable from astart-up jump with the result that, upon releasing the clutch, thevehicle starts with a jump, which is particularly unacceptable forsafety reasons for mobile working devices.

Starting from this prior art, the object of the invention is to furtherimprove the known valve solutions while retaining their advantages sothat, at least for use in a clutch, the start-up jumps described aboveare avoided, while the valve should be economical in its implementationand functionally reliable in operation.

This object is achieved by a valve having the features of claim 1 in itsentirety.

Due to the fact that, according to the characterizing portion of claim1, the respective differential pressure that arises during the flowthrough the further fluid-carrying connection between the utility portand the tank port acts on the valve piston by means of a control devicein such a way that it acts against a stop position, from which thefurther fluid-carrying connection is noticeably inhibited, to arrive ata fully open port position, in which, compared to the stop position, anenlarged opening cross-section from utility port to tank port isachieved, an opportunity is created to increase the valve piston strokewithout having to accept the start-up jump of the PI characteristicline. Thus, the valve of the invention can produce a very large openingcross-section upon release of the clutch and thus ensure a rapidseparation of the coupling.

The valve according to the invention need not be limited to applicationsin clutches, but rather can be generally used where, for space and/orcost reasons, only small actuator devices in the form of actuatingmagnets can be used while simultaneously increasing the free travel pathof the valve piston beyond the possible operating range of the actuatingmagnet in order to thus arrive at very large opening cross-sections,which, apart from improved fluid removal, also serve to supply largerfluid amounts to hydraulic systems.

It is preferably provided that the control device carries the respectivedifferential pressure, by means of a control duct preferably arranged inthe valve housing, to a piston ring surface of the otherwisepressure-equalized valve piston, which, starting from the stop position,reaches the fully open port position under the influence of thisdifferential pressure. The mentioned pressure regulation is carried outwith the help of the pressure effect on this piston ring surface,preferably designed as an annular surface. Furthermore, it is providedthat the stop position is formed by a disc-shaped stop element, which ispressurized by an energy accumulator, preferably by a compressionspring, wherein the stop element is supported in its stop position onfixed parts of the valve housing or the actuating magnet.

As set forth above and as is common for other comparable valveconstructions, the spring force of said energy accumulator is not passeddirectly to the valve piston forming the regulating piston. It is truethat, in the valve solution according to the invention, a stop element,preferably formed as a disc, is incorporated, as usual, between thevalve piston and the compression spring, wherein the stop elementnormally moves synchronously with the valve piston while transferringthe spring force in order to move the valve piston to its initialposition when the actuating magnet is not energized; however, the valvepiston can continue to move and thus enable a larger openingcross-section by reaching its fully open port position opening beyondsaid stop position under control of the differential pressure. Thepertinent further movement takes place without the support of the springforce, only under the influence of the differential pressure, whichinevitably arises during the flow through the valve from the utilityport to the tank port.

As set forth above, the clutch is thus relieved with fluid connection tothe tank port by switching off the actuating magnet. The mentionedspring force hereby presses the valve piston into a position whichpermits the flow from the utility port, i.e. the clutch load, to thetank port and the disc-shaped stop element abuts the pole core of theactuating magnet. As a result of the differential pressure acting on theannular surface of the valve piston, the piston is now moved in thedirection of the actuating magnet, but without the spring force, and assoon as the clutch is completely emptied, the differential pressure, andhence the force acting on the valve piston, is eliminated.

The valve piston is now in a so-called indifferent state and, whenswitching on the electric actuating magnet again, a minimum magneticforce is now sufficient to move the piston back to the point of contactwith the stop disc. A low actuation force of the magnet in the nonlinearregion is thus sufficient to be able to move the piston out of thisindifferent region. As soon as the contact point with the return springhas been reached, the electrical magnet or actuating magnet is in itslinear region and the mentioned PI characteristic line can be runthrough cleanly without a start-up jump, ensuring a smooth engagement.The invention thus provides the use of an inexpensive actuating magnetwith a low linear stroke range, yet achieving high magnetic forcewithout limiting the valve stroke, which is so important for thelow-loss flow.

The valve solution according to the invention is explained in greaterdetail below based on an exemplary embodiment according to the drawing.

It is shown in a basic representation, not to scale, in the figures:

FIG. 1 shows the complete valve, formed as a proportional pressureregulating valve, by way of a longitudinal section;

FIG. 2 shows an enlarged figure section of FIG. 1, showing the valve ina relief position, with a partially opened fluid connection from theutility port A to the tank port T without overtravel;

FIG. 3 is a longitudinal section representation corresponding to FIG. 1,wherein the valve is shown in the overtravel position with an enlargedopening cross-section from utility port A to tank port T; and

FIG. 4 an enlarged figure section of FIG. 3, corresponding to FIG. 2,but with a control duct, closed by a plug, drawn in on the oppositeside.

The valve shown in the figures is formed as a proportional pressureregulating valve. The valve includes a valve piston 12, longitudinallydisplaceably guided in a valve housing 10. The valve or control piston12 is controllable by means of an actuator device 14 in the form of aso-called actuating magnet for assuming its individual movementpositions. The actuating magnet 14 is designed according to the priorart and includes a coil winding 20, energizable by means of a plug 18,for moving a magnet armature 16. The actuating magnet 14 is designed asa so-called push magnet, i.e., when current flows through the coilwinding 20, the magnet armature 16 moves downward in viewing directionon FIG. 1, and, with the one free end of the valve piston 12, exerts aforce on the same via its actuating plunger 22, which abuts with itsfree front end, thus triggering a movement of the valve piston 12.

The actuating magnet 14 is designed to be pressure-tight and its polecore 24 opens into a flange plate 26 at its end, by means of which thecomplete valve can be affixed to a valve or control block, not shown. Infront of the corresponding port on such a complete valve or controlblock, the valve housing, on its outer circumference, is designed as aplugged part in cartridge design and, on its outer circumference,equipped with sealing rings for the connection to the correspondingfluid connection points in the valve or control block.

In particular, for this purpose, the valve housing 10 includes apressure supply port P and a utility port A in radial direction and atank port T at the free front end of the valve housing 10, viewed inaxial direction. Via the pressure supply port P, a hydraulic fluid of apredeterminable amount and a predeterminable pressure, for exampleprovided by a hydraulic pump (not shown), can be supplied, for example,to its other ports A, T. For the herein particularly preferred mentioneduse of the valve in clutches, the utility port A is connected to apertinent clutch device (not shown). If a tank port T is concerned here,this can also concern a common return line, which need not necessarilyopen into a storage tank, but which at least needs to have a lowerpressure, for example, of the magnitude of the tank or ambient pressure,which is generally lower than the pressure at the pressure supply port Por at the utility port A.

The design of a valve as described above is known. In contrast, thesolution according to the invention distinguishes itself, inter alia, bythe fact that the respective differential pressure created when flowingthrough the fluid-carrying connection between the utility port A and thetank port T, acts on the valve piston 12 in such a way that it actsagainst a stop position 32 by means of a control device 30 to reach, inaccordance with the representation of FIG. 1, a fully open port positionin which an enlarged opening cross-section from utility port A to tankport T (see FIG. 3) is reached, compared to the stop position 32 (seeFIG. 1).

For this purpose, the control device 30 includes a control duct 34,extending in the axial direction in the valve housing 10, which guidesthe respective differential pressure to a piston ring surface 36 of theotherwise pressure-equalized valve piston 12, which, starting from thestop position 32, can move to the fully open port position (see FIG. 3)under the influence of this differential pressure.

The mentioned pressure-effective piston ring surface 36 results from thedifference in diameter d₁−d₂ (see FIG. 2) of the valve piston 12 in itsupper stepped recess region. The control duct 34 opens into adiametrally expanded fluid chamber 38 of the valve housing 10, in which,in every movement position of the valve piston 12, its one piston ringsurface 36 is guided, which, as previously mentioned, results from astepped transition of different piston diameters d₁/d₂ of the valvepiston 12, which tapers in this way in the direction of the tank port T.

Viewed in the direction on FIGS. 1 and 2, the control duct 34, at itsupper free end, opens in axial direction from the valve housing 10 outof its free end face where it is sealed by a closure plug 40. At thelower end at a transverse guide, the control duct 34 opens into theconnection point A′ at which the respective pressure between utilityport A and tank port T is permanently present via the valve or controlblock, not shown. The pressure A′ here corresponds to the pressure A. Ifthe control duct 34 is closed at its upper end by the closure plug 40,it at least leaves a connection between the control duct 34 and thefluid chamber 38. In order to be able to seal the fluid chamber 38against the actuating magnet 14 as well as against the pressure supplyport P, the valve piston, on its outer circumference, has duct-likefluid seals of conventional design as well as a pressure centeringgroove 42.

The previously mentioned stop position 32 is essentially formed by meansof a disc-shaped stop element 46, pressurized by an energy accumulatorin the form of a compression spring 44, wherein the stop element 46 issupported for this purpose on the fixed parts of the actuating magnet 14in the form of the pole core 24. To receive the compression spring 44,the pole core 24 has a cylindrical chamber-like recess 48, which tapersdown in diameter towards the free end of the actuating plunger 22 inorder to form a stop shoulder 50, against which the disc 46 can abut thefront end.

As shown in the figures, the valve piston 12 with its tapered diameterend 52 penetrates a cylindrical central recess of the disc-shaped stopelement 46 and, in the region of its free end 52, has a diameterwidening in the manner of a catch 54 which, as shown in FIGS. 1 and 2,overlaps the disc 46 from above while abutting the same. By operatingthe actuator device 14, the stop element 46 is moved against the actionof the energy accumulator in the form of the compression spring 44 outof the stop position 32 to a maximum possible effective position inwhich the fluid-carrying connection between the supply port P and theutility port A is established and the connection between utility port Aand tank port T is completely blocked (not shown). In this valveposition, the clutch, which is connected to the utility port A, can thenbe supplied with a fluid of predeterminable pressure in apredeterminable amount from the pressure supply port P, and, asdescribed above, the clutch plates can then be gradually brought intocontact, while overcoming clutch spring forces, for the purpose oftransmitting torque through friction.

In order to establish complete pressure equalization both within theactuating magnet 14 and for the valve piston 12, both the valve piston12 and the rod-shaped actuating element 22 in the form of the actuatingplunger are provided with a continuous pressure-equalizing duct 56 that,at its one free end, opens in the direction of the tank port T and, atits other free end, comes into abutment with parts of the movable magnetarmature 16. As further shown in the individual figures, the pressureequalization duct 56 opens via a transverse bore 58 into the cylindricalrecess 48, which forms the spring chamber for the compression spring 44inside the pole core 24. The compression spring 44, with its upper freeend when viewed in the direction on figures, is in direct contact withthe disc-shaped stop element 46 and, with its other lower end, is incontact with a termination disc 60, which is affixed pressure-tightbetween one free end of the valve housing 10 and the adjacent front endof the pole core 24.

When assuming the stop position 32, the valve piston 12 has a furtherreduction in diameter 62 with an axial length such that at least thesupply port P can be open and the utility port A can be blocked by thevalve piston 12, wherein, when moving the valve piston 12 under theinfluence of the actuator device 14 in the direction of the tank port T,i.e. downward in viewing direction on the figures, the connectionbetween supply port P and utility port A is increasingly established andthe connection of the supply port A to tank port T is blocked.

To disengage the clutch, not shown, it must be relieved with fluidconnection to the tank port T, to which end the actuating magnet 14 mustbe turned off first. The spring force of the compression spring 44 herepushes the valve piston 12 into a position which allows the flow fromutility port A to tank port T, wherein the disc 46 moves against thepole core 24, assuming the stop position 32. The respective valve-reliefposition of utility port A to tank port T without overtravel is shown inFIGS. 1 and 2.

However, starting from this stop position 32, the valve piston 12 cannow continue to move upwards, according to the representations accordingto FIGS. 3 and 4, wherein the catch 54 is removed from the upper face ofthe disc 46, thereby allowing for a larger opening cross-section betweenthe utility port A and the tank port T. FIGS. 3 and 4 show the valve inthe respective overtravel position. This overtravel of the valve piston12 takes place without the support of the spring force of thecompression spring 44 by taking advantage of the differential pressureat the connection point A of the control duct 34 that inevitably arisesduring the flow through the valve from utility port A to the tank portT. This differential pressure at the connection point A acts on theannular surface 36 of the piston 12 and, without the spring force, movesit further upward in the viewing direction in FIGS. 3 and 4.

When the clutch is completely emptied of fluid by the clutch springsagain bringing the individual clutch discs to a distance from eachother, the differential pressure, and hence the force effect on thevalve piston 12, is eliminated. The valve piston 12 is thus in anindifferent state and, when switching on the actuating magnet 14 again,a minimal force is now sufficient to return the valve piston 12 to thepoint of contact with the disc 46, whereby the catch 54 again abuts thedisc 46. If this point of contact is reached with the compression spring44, as shown in FIGS. 1 and 2, the actuating magnet or electromagnet 14is in its linear region, so that the so-called PI characteristic linecan be run through cleanly without a start-up jump. As shown inparticular in FIG. 4, the fluid chamber 38 is conically tapered towardsthe top, so that a conical transition region 64 is formed between fluidchamber 38, significantly enlarged in diameter, with respect to thediameter d₁ of the valve piston 12 within its valve housing 10.

Overall, the valve construction according to the invention thus achievesthe use of an inexpensive actuating magnet with a low linear strokerange, thus achieving high magnetic force without limiting the fullvalve stroke, which is so important for the low-loss flow.

1. A valve, in particular a proportional pressure regulating valve,having a valve piston (12) longitudinally displaceably guided in a valvehousing (10) and controllable by means of an actuator device (14), saidvalve housing (10) having a plurality of fluid ports (P, A, T) andwherein, in a movement position of the valve piston (12), afluid-carrying connection between a pressure supply port (P) and autility port (A) is established and, in another movement position,another fluid-carrying connection between the utility port (A) and atank port (T) is established, characterized in that the respectivedifferential pressure, created when flowing through the furtherfluid-carrying connection between the utility port (A) and the tank port(T), acts on the valve piston (12) by means of a control device (30) insuch a way, that the valve piston (12) acts against a stop position(32), from which the further fluid-carrying connection is noticeablyinhibited, to arrive at a fully open port position in which, compared tothe stop position (32), an enlarged opening cross-section from utilityport (A) to tank port (T) is achieved.
 2. The valve according to claim1, characterized in that the control device (30) carries the respectivedifferential pressure, by means of a control duct (34) preferablyarranged in the valve housing (10), to a piston ring surface (36) of theotherwise pressure-equalized valve piston (12), which, starting from thestop position (32), reaches the fully open port position (FIG. 3) underthe influence of this differential pressure.
 3. The valve according toclaim 1, characterized in that the stop position (32) is formed by astop element (46) pressurized by means of an energy accumulator,preferably by a compression spring (44), wherein the stop element (46)is supported on fixed parts of the valve housing (10) or actuator device(14).
 4. The valve according to claim 1, characterized in that the stopelement is formed of a disc (46) with a central recess, that the disc(46) in the stop position (32) on its front end is supported on the polecore (24) of the actuating magnet (14) and that the compression spring(44), with its one free end, is supported on the disc (46) and, with itsother free end, is supported on a termination disc (60) affixed betweenthe valve housing (10) and the pole core (24).
 5. The valve according toclaim 1, characterized in that the valve piston (12) with its one freeend (52) penetrates the stop element (46) and in the region of this freeend (52) has a catch (54), which, upon actuating the actuator device(14), moves the stop element (46) against the action of the energyaccumulator (44) from the stop position (32) to a maximum possibleeffective position, in which the fluid-carrying connection between thesupply port (P) and the utility port (A) is established and theconnection from utility port (A) to tank port (T) is blocked.
 6. Thevalve according to claim 1, characterized in that the actuator device(14) is formed of a push-action actuating magnet and that both the valvepiston (12) and the rod-shaped actuating element (22) of the actuatingmagnet (14) have a continuous pressure-equalizing duct (56), which openson one side thereof into the tank port (T), regardless of the movementposition of the valve piston (12).
 7. The valve according to claim 1,characterized in that the control duct (34) opens into a diametricallyexpanded fluid chamber (38) of the valve housing (10), in which, inevery movement position of the valve piston (12), its one piston ringsurface (36) is guided, which results from a stepped transition ofdifferent piston diameters (d1/d2) of the valve piston (12), whichtapers in this way in the direction of the tank port (T).
 8. The valveaccording to claim 1, characterized in that the control duct (34), atits one end-side outlet from the valve housing (10), is closed by aclosure plug (40) in this region, which keeps the inlet of the controlduct (34) into the fluid chamber (38) free, and that the other end ofthe control duct opens into a connection point (A′), which picks up thedifferential pressure between the utility port (A) and the tank port(T).
 9. The valve according to claim 1, characterized in that whenassuming the stop position (32), the valve piston (12) has a furtherreduction in diameter (62) with an axial length such that the supplyport (P) is opened and the utility port (A) is blocked by the valvepiston (12), wherein, when moving the valve piston (12) under theinfluence of the actuator device (14) in the direction of the tank port(T), the fluid-carrying connection between the supply port (P) andutility port (A) is increasingly established.
 10. An application of avalve according to an embodiment according to claim 1 in a clutch,comprising at least two clutch discs which, in the coupled state,establish a frictional connection with each other against the action ofa clutch energy accumulator under the actuating pressure at the utilityport (A) of the actuated valve and, in the uncoupled state, under theinfluence of the clutch energy accumulator, pushes operating fluid fromthe utility port (A) to the tank port (T) with the valve not beingactuated, having a first opening cross-section until reaching the stopposition (32) and having a comparatively larger opening cross-sectionwith further movement of the valve piston (12) away from the stopposition (32) in the direction of the armature (16) of the actuatordevice (14).
 11. The application according to claim 10, characterized inthat, after complete decoupling, the valve piston (12) is in anindifferent state so that, when actuating the clutch by switching on theactuator device (14) again, a minimum magnetic force is sufficient tomove the valve piston (12) into its stop position to make contact withthe stop element (14, 40).